Isoimmunization of female rabbits with a soluable extract from rabbit sperm after treatment with lithium diiodosalicyclate resulted in a high degree of fertilization inhibition. A preparation from extracted sperm by a non-ionic detergent, however, induced post-fertilization infertility. The experimental plan is to identify, purify, and characterize the sperm antigens responsible for these antifertility effects in rabbits. The antigens will be purified through a series of biochemical and chromatographic methods including gel filtration, ion exchange, affinity chromatography and preparative gel electrophoresis. Antigen purity will be followed by immunodiffusion, disc gel electrophoresis and antibody absorption studies.